Activating Vertices and Edges selecting modes simultaneously
In 3D View, you can change your selection mode by clicking the related buttons (check the image) you can activate 1 selection mode, or 2 by pressing Shift and clicking the related button, or you can activate all of them using the same method, so you can activate Vertices, Edges and Faces selection modes at the same time.
In the image you can see I have both Vertices and Edges selection modes activated.